I've since sent her my thoughts on what is likely to have happened, which I'll post here:
The 200-level course number suggest to me that the class as a sophomore-level organic chemistry class. A pretty common experiment in a class like that is to combine concentrated nitric & sulfuric acids, and use the resulting mixture to nitrate an aromatic compound, usually toluene. Both stages of this process give off a LOT of heat, and the whole sequence is usually done directly over ice.
If there's any leftover nitrating mixture, it usually gets at least somewhat neutralized before being rinsed down the drain with lots and lots and lots of water. (In my previous career as a high school chemistry teacher, I've done something similar using filter paper to make flash paper.)
The fire department report you linked me to makes me think that some student disposed of the extra nitrating mixture in a container of hydrocarbons of some kind or another. If there were any aromatic compounds in the container, the leftover NO2(+) ions would likely have started to react with them. I'm guessing that the heat given off in the reaction probably ignited the waste, and (if the container was capped) may have caused a pressure build-up explosion.
I've linked you to everything that I know about the accident right now, but the scenario I described above hangs together reasonably well for me. If I see an update from C&E News later in the week, I'll try to follow up.